1) Field of the Invention
This invention relates generally to pumps, and in particular to a regenerative fuel pump having a vaned impeller. Such a pump is useful as an electric-motor-operated fuel pump for an automotive vehicle to pump liquid fuel from a fuel tank through a fuel handling system to an engine that powers the vehicle.
2) Background Information
In an automotive vehicle that is powered by an internal combustion engine, fuel may be pumped through a fuel handling system of the engine by an in-tank, electric-motor-operated fuel pump.
Examples of fuel pumps are shown in various patents, including U.S. Pat. Nos. 3,851,998; 5,310,308; 5,409,357; 5,415,521; 5,551,875; and 5,601,398. Commonly owned U.S. Pat. Nos. 5,310,308; 5,409,357; and 5,551,835 disclose pumps of the general type to which the present invention relates, and such pumps provide certain benefits and advantages over certain other types of pumps.
For developing pressures suitable for a vehicle fuel system, the impeller of a regenerative pump may have very close running tolerances to the walls of the pump parts that axially confront opposite faces of the impeller internally of the pump. Hence, dimensional stability of materials is an important design consideration, and certain materials have been found particularly suitable for the impeller and for the parts of the pump (a pump cover and a pump body, for example) that confront it. PPS and phenolic are examples of suitable impeller materials; those two materials, as well as aluminum, are suitable for the pump cover and pump body.
A representative pump is a wet pump that comprises an inlet in the pump cover and an outlet in the pump body. The inlet and the outlet are open to an annular pumping chamber that runs around the perimeter of the pump. The impeller comprises vanes that rotate within the pumping chamber to move fluid from the inlet to the outlet. When the pump is disposed within a fuel tank with its axis generally vertical and the cover facing a bottom wall of the tank, the inlet is open to liquid fuel in the tank. When the pump is operated by an associated electric motor, some pressure difference is developed across those portions of the impeller faces which are disposed radially inward of the annular pumping chamber and which have close running fits to confronting wall surfaces of the pump cover and the pump body, thus creating a force imbalance that acts on the impeller in a downward direction. The force of gravity is additive to that downward force imbalance. Force imbalance may act on an impeller in ways that increase running friction. Such friction may decrease pump efficiency and accelerate wear that leads to even further loss of pumping efficiency.
Various solutions have been proposed to minimize, and ideally eliminate, force imbalance acting on the impeller. Examples are found in U.S. Pat. Nos. 3,768,920; 4,586,877; 4,854,830; 4,872,806; 5,137,418; and 5,607,283.